1. Field of the Invention
This invention relates to an interconnection circuit for a network of data stations and more particularly to such an interconnection circuit for a network wherein control of the transmission between stations is shared by the respective stations.
2. Description of the Prior Art
Prior art networks not having a master controller have employed "contention" schemes whereby each node of the network contends for the transmission medium whenever it is ready to transmit. One of the earliest contention networks was the "Aloha" system built by the University of Hawaii. In this system, each node transmitted whenever it had a packet ready for transmission. Whenever a portion of one node's transmission overlapped with another node's transmission, that overlap destroyed both packets. If the sending node did not receive an acknowledgment within another packet from the destination node after an arbitrary time period, it would assume that a collision had occurred and retransmit. In order to avoid continuously repeated collisions, some method of introducing a random retransmission delay had to be introduced.
An attempt at reducing the effect of collision in contention-type networks is disclosed in the Metcalfe et al U.S. Pat. No. 4,063,220 which is directed toward a communication network in which each node is capable of detecting when collision occurs on the channel during that node's transmission, and interrupts its transmission when such a collision occurs. A random number generator is employed to select an interval of time to delay before the next attempt at transmission. However, the collision detection mechanism adds to the complexity of the respective nodes with an increase in the cost of the system.
An improvement in the avoidance of collision problems is disclosed in U.S. Pat. No. 4,332,027 entitled Local Area Contention Network Data Communication System, and assigned to the assignee of the present invention. That application discloses a network employing a plurality of stations where each station is adapted to operate in a cyclic mode for contending for access to the network channel along with other stations of the network. The three states of the cycle are the Idle state, the Packet-Being-Transmitted state, and the Acknowledgment Period state. Each station will not begin transmission until it determines that the channel is in an Idle state. Once the station has determined that the channel is idle, it will then delay for a period of time that is randomly chosen and, if the channel is still idle, will then begin transmission. Following transmission, the channel will again be quiescent for a short period of time before the acknowledgment signal is transmitted from the receiver. Each packet of data to be transmitted is of fixed length so as to provide for the synchronization between the various stations contending for access to the channel.
The collision problem still arises when two separate networks are interconnected for expansion of the system. A particular problem arises in such interconnection when a station on one network is attempting to access the combined network while a station on the other network is also attempting to access the combined network. For the Metcalfe et al type system, a repeater is provided which returns the respective transmissions to their senders creating collisions on each channel which the respective senders detect and stop transmission. Such a repeater is disclosed in the Boggs et al U.S. Pat. No. 4,099,024. However, the repeater of Boggs et al is not adapted to handle transmissions from stations on opposite sides, which stations are not adapted to detect collisions and stop transmission.
It is, then, an object of the present invention to provide improved interconnection circuitry for two local area contention networks.
It is another object of the present invention to provide an improved interconnection circuitry for two local area contention networks, the stations of which are not adapted to cease transmission after detecting a collision on the combined network with transmissions from a competing station.
It is still a further object of the present invention to provide an improved interconnection circuitry for two local area contention networks, which circuitry jams competing transmissions from opposite sides of the interconnect circuitry.